The mouth is the opening that forms the beginning of the alimentary canal and through which food enters the digestive process. The upper region of the mouth is called the palate, the front part being hard and immobile while at the back lies the mobile soft palate. The tongue is situated behind the lower teeth, and salivary glands secrete saliva into the mouth through small ducts. Saliva contains the enzyme ptyalin, which begins the breakdown of starch, while the chewing action of the teeth and manipulation with the tongue reduce the food to a more manageable consistency so that it can be swallowed.

When undigested food reaches the small intestine, it increases the heat in the small intestine which produces mouth or tongue ulcers. Therefore one must avoid rich food till the digestive system recovers.